1. Field of the Invention
The present invention relates to an improvement in a drive control device for a motor actuator for use with an automobile air conditioner, for example.
2. Description of the Prior Art
In recent years, the automobile air conditioner is automatically controlled, and in association therewith, it is known that an intake door, mix door and various outlet doors installed in the automobile air conditioner are driven by motor actuator.
Generally, the motor actuator is controlled by an exclusive drive control device, and such a conventional drive control device for the motor actuator is disclosed in Japanese Utility Model Publication No. 60-645, which device employs relays.
The conventional drive control device for the motor actuator is shown in FIG. 6. Referring to FIG. 6, the drive control device is generally composed of a drive unit for driving the doors and a control unit for controlling the operation of the drive unit.
The drive unit is constituted of a motor 10 functioning as a drive source for driving the doors and a moving member 20 for transmitting a torque of the motor 10 through a gear mechanism 15, converting the torque to a reciprocating motion, and driving the doors mechanically connected to the moving member 20. On the other hand, the control unit is constituted of an electrode pattern 30 including a first strip electrode 25, a second strip electrode 26 and a non-conductive portion 27 which are formed on the surface of the moving member 20, control switches 40 to 43 connected at respective one ends with sliding contacts 31 to 34 slidingly contacting with the electrode pattern 30 and grounded at respective other ends, and relays 45 and 46 connected at respective one ends with sliding contacts 35 and 36 slidingly contacting with the electrode pattern 30 and connected at respective other ends with a power source 50, and contacts 45A and 46A adapted to be operated according to the operation of the relays 45 and 46 and supply current to the motor 10. The first strip electrode 25 and the second strip electrode 26 are formed of a metal plate primarily containing copper, while the sliding contacts 31 to 36 are formed by a conductive brush primarily containing carbon. Thus, there is provided a switch of a type such that the movement of the moving member 20 causes the sliding motion between the metal plate and the brush.
Accordingly, when any of the control switches 40 to 43 is turned on, the moving member 20 is moved to a predetermined position, thereby driving an intake door, mix door and various air outlet doors installed in the automobile air conditioner through a door link (not shown) and adjusting an air conditioning mode and the like of the air conditioner.
For example, when the control switch 40 is turned on under the condition shown in FIG. 6, the control switch 41 is turned off in association therewith. As a result, there is formed a closed circuit for a control system allowing the current to flow from the positive terminal of the power source 50 through the relay 45, the sliding contact 35, the first strip electrode 25, the sliding contact 31, the control switch 40 to the negative terminal of the power source 50. Accordingly, the relay 45 is operated to move the contact 45A in a direction depicted by arrow in FIG. 6 and thereby close the same. Accordingly, the current flows from the positive terminal of the power source 50 to the motor 10 in a direction depicted by arrow in FIG. 6, and the motor 10 is rotated in a direction corresponding to this current direction. The rotation of the motor 10 causes the movement of the moving member 20 through the gear mechanism 15 in a direction depicted by arrow B in FIG. 6, and simultaneously causes a relative movement of the sliding contact 31 in a direction depicted by arrow C. The movement of the moving member 20 causes the door link mechanically connected thereto to be driven to rotate the intake door, the mix door and the various air outlet doors. When the sliding contact 31 reaches the non-conductive portion 27 during the movement of the moving member 20, the closed circuit of the control system is opened to thereby make the relay 45 inoperative and open the contact 45 A.
As a result, the motor 10 is stopped to thereby set a desired air conditioning mode and the like of the automobile air conditioner.
However, in the above-mentioned drive control device for the motor actuator, since the control unit includes the relays, it is advantageous in such that a voltage drop in the circuit from the power source 50 to the motor 10 is less, but there is a shortcoming that the control unit has a less resistance against vibration since the relay is a mechanical component. This shortcoming is of a great significance from a viewpoint of reliability of the drive control device for the motor actuator in an automobile to which various vibrations are applied in running.
The conventional drive control device for the motor actuator has another shortcoming such that it is limited to make the relay compact since it is a mechanical component, and that a plurality of brushes functioning as the sliding contacts are used. That is, the production of a compact motor actuator to be installed in a limited space of an automobile is dependent upon the use of a compact relay and the number of brush. Therefore, it is very difficult to make compact the motor actuator using the relay, causing a problem such that a production cost of the motor actuator cannot be reduced down to a certain value.